Radioreceiver



May 9, 1933 v w. F1coTTER 1,908,119

RADIORECEIVER Filed May 24, 1932 INVENTOR Wilma, F unen Patented May 9, 1933 WILLIAM F. co'r'rnn, or' SPRINGFIELD,

MASSACHUSETTS, ASSIGNOR TO UNITED AMERICAN BOSCH CORPORATION, OF SPRINGFIELD, MASSACHUSETTS, A CORPORA- TION OF NEW-YORK RADIORECEIVER Appncanon mea May 24, 1932. serial No. 613,215.

My invention relates to improvements in radio receivers; and especially radio receivers to operate on two or more bands of frequencies or wavelengths.

lllhis invention has Jfor one of its objects to provide means for increasing the sensitivity of radio receiving apparatus.

j Another object of the invention is to provide a convenient arrangement by which the l@ radio frequency output of the detector tube of the receiver can be more easily filtered. `@n account of the slope of the sensitivity curve on the high frequency end of the band of longer wavelengths, this filtering isvapt llt to be more or less difficult to accomplish.

rlhe advantages of the invention are fully set-forth in the ensuing description, with the accompanying drawing; but the disclosure is illustrative onlyj and changes may be made d@ without departing :trom the principle of the invention. j

'lhe figure shows a circuit for a receiver according to my invention.

rllhe receiver comprises electric circuits 25 containing vacuum tubes in parallelin the output ot the audio 'frequency amplification stage, a suitable detector and several stages of radio frequency amplilication disposed to operate on the resistance-repeater principle,

3U with tuned circuits for selectivity; and a rectifier to enable ordinary lighting or power mains to vserve as sources of electrical energy for the cathodes and anodes of the vac num tubes.

3% l show an antenna 5y at one end of a resistance 6 having an adjustable contact 7 connected to ground. The antenna is also joined to one end of' a variable electrical condenser 9, the other pole of which is connectt@ ed to the grid of the first vacuum tube member or amplifier A. The other end ot the resistance 6 is connected to the cathode in the .ibo A, this tube being of the screen* 'grid type, with a unipotential cathode 45 grounded through a fixed condenser 14. The shield or screen in the tube A is grounded through a condenser 17. Attached to the lead between the grid of the tube A and condenser 9 is a coil including a pair of sections 10 and 11, these sections being in series and grounded. 'lhey are also associated with an adjustable condenser 12 connected to the grid of the tube A at one end and grounded at the other. rlhe sections 10 and 11 and condenser 12 constitute a tuning circuit, and the tube A as shown is joined to the antenna by a resistance coupling because of the presence of the element 6. W' hen the receiver is to be used for waves of the longer length, both sections 10 and 11 together with the condenser 12 are put into circuit. But when the band of shorter wave lengths is to be employed, the section 11 can be cut out by bridging the terminals 18 connected to the two ends of the section 11 by suitable switch mechanism. @t course, more than two sections may be utilized it operation is desired on more than two bands of wave lengths.

rlhe second radio-frequency amplifier tube A-l is of the same description as the first 70 tube and is connected to the first tube by a conductor entending between the plate of the first tube and the grid ot the second, with a xed condenser in the line thereof. lThe cathode of tube A-l is also connected to resistance 6 and grounded by way ot condenser 141; and the screen by way of condenser 17. Between the condenser. 15 and the grid of the tube A-,1 is a tuned circuit consisting again of a coil in two sections 10 and 11 in series and grounded, together with another adjustable grounded condenser 12 connected to the ygrid of tube A-1; the section 11 having contacts 13 joined to its extremities, so that this coil can be switched 85 ,out at the same time as the i'lrst coil 11.

Between the condenser 15 and the "plate i of' the rst amplifier `tube A is joined one end of the resistance 16 across which the plate circuit load is developed; this resistance 16 having capacity-coupling through the condenser 15 with the tuning circuit between the amplifiers A and A-1.

The same connections exist between the plate of the tube A-l and the grid of the radio frequency amplifier tube A-2, except that the screen of the latter is grounded through an additional condenser 17a; and the `cathode of this third tube is directly joined to one end of a resistance 18 and con- 100 denser 19 in parallel, the opposite terminals f tions. The resistance 18 of t e cathode of tube Amt is for grid bias purposes. The

aforesaid coupling resistances 16 are connected to the condenser 17 through a suitable resistance element 36.

The last stage in the circuits of the receiver comprises a detector tube a, and two audio frequency amplifiers a-1 in parallel. The same coupling with tuning circuit as before is used to unite the tubes A--2 and a, and comprises the resistance 16. A resistance 18a and a condenser 19a, grounded in parallel, are connected with the cathode of the tube a. In the output of this tube a is a radio frequency choke coil 33, and the primary coil 32 of a transformer, together with a grounded fixed condenser 12. i A common lead 34 connects this coil 32 and all ofthe resistance coils 16. The tubes a-l have each a suppressor grid connected to the filament therein.

To supply current to the plates of. all the tubes, the common conductor 34 is connected by leads 28 and 30 to the heated cathode of a rectifier 20. This rectifierYV also containsA twoanodes each united to the outer terminal of-a pair of seconda coils 21 and 22 in series. The cathode o the rectifier is heated by current. from a secondary 23, and a secondary coil 24 supplies current tothe heaters of the cathodes of the tubes A, A--1,

A-2 and a, and the filaments of the tubes a-L .All of these secondaries are mounted upon the same iron core to be ener ed from the prima?` 25 connected to a lig t or power circuit. rom the junction point of the coils A21 and 22 is led a conductor 2 6 in series with an iron core inductance 27, having condensers 29 in shunt therewith and the conductor 28. A tap 42 leads from the coil 27 to a similar coil 41 connected by a lead 40 to a secondary 44 coupled to the coil 32. Coil 41 will be the field winding of a dynamic loud speaker. This coil 41 lis also joined to a grounded resistance 52, -with a condenser 51 between its grounded end and the supplyl lead 28. At 43 is a resistance in series wit the secondary 44.

The gridsv of the audio ampliertubes a are united'to the tube a by transformer coupling byl being joined to one terminal of the secondary 44 which is wound on an iron core with the coil 32. These tubes are both pentode tubes, with ltheirfscreens joined to -lead. 34 by a lead 48. Between the resistance .43 and coil 44 is connectedone pole of a condenser 45, the other pole 0f whichy is f 1mi peint of the windings 46 to allow for alternating current *Huctuations of the heating nnen. The plats of the tubes nel.

are connected to one terminal of the primary coil 49 of an iron core transformer, the secondary 50 of which is to have its terminals connected to the movable coil of the dynamic loud speaker. A lead 47 connects the other end of the primary 49 to the su ply leads 23 and 30, hence the coils 32 an 49 and all the resistances 16 are in multiple.

This receiving set operates very similar to the set mentioned in the aforesaid application. For the shorter wavelen h ran the coils 11 are switched out, whi e for t e band of longer lwavelengths they are con nected in. The arrangement of audio amplifyin tubes a in parallel, connected throng transformer coupling to the detector a increases thesensitivity of the set to a desirable level. A The radio fre uency currents in the output circuit of t e detector tu yare filtered out bythe condenser 12 and co1 33.

The numeral 37 indicates a resistance in series with a resistance 36 on the one hand and a grounded resistance 38 on the other; 39 being a similar! resistance connected to the resistance 6 and the common terminal of resistances 37 and 38.

The current flowing in the resistance 52 is mainly direct current and a potential drop exists between the terminals of this resistance, which is in the return circuitto the rectifier 2 0. Hence the grids of the audio freuency amplifiers a-1 are negatively biase and any alternating current in the resistance 52 is filtered and smoothed out by the resistance 43 and condenser 45. The resistance 43 is about 100,000 ohms, and condenser 45 has about 0.1 microfarad capacity. Thus a high capacity by-pass condenser is not needed.

The resistance-condenser couplin with tuned circuits described herein invo ves resistanc such as resistors 16 of no greater .value than of the order of 25,000 ohms; while the capacity of the condensers 15 is. of the order of 25 micromicrofarads.

Havin described the invention, what is claimed 1s;

A radio receiver having an audio am lier tube, al1-electric circuit and a source o electrical ener for energizing the anode thereof, said 'circuit comprising filtering condensers and inductances and an ohmic resister in circuit with said inductanoes and disposed in the return side of said circuit,

e connection at one end of said resistor for biasin the 'd in said tube, a second resistor 1n sai connection, a. condenser connected to the second resistor, and to the fila- 5 ment circuit of said tube, and a ground conneetion between said second condenser and said filament circuit, said second condenser and last-namedrresistor forming a circuit to` filter out' alternating current oscillations from the'connection between said resistors and the'grid.

In testimony whereof I ox my si ature.

c WILLIAM F. COT ER,

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